1. Field of Invention
The present invention relates to fuel injection in general and in particular to a method and apparatus for the injection of liquid and gaseous fuels directly into the combustion chamber of an engine.
2. Description of Related Art
The book, The Modern Diesel Engine, (Geoffrey Smith, Ed., Ilife and Sons Ltd, London, 1942) describes the most advanced practical and experimental diesel engine technology up to about 1942. The Ricardo Comet, Lanova air-cell and Acro air-cell systems use a small side chamber connected to the main combustion chamber by a small passage. When the piston moves down, the high pressure gases stored in the side chamber rush through the passage to the main chamber, creating a high-velocity jet that may be used for atomization and mixing of the jet. Cummins Engine Co. produced engines in the 1930's with an air-cell in the piston, which produced an air jet aimed directly at the fuel injector, supposedly improving the air supply to the burning fuel.
U.S. Pat. No. 6,564,770 B1, May 2003 (Geoffrey Cathcart, assigned to Orbital Engine Company) discloses a “Method of Injection of a Fuel-Gas Mixture to an Engine”. This patent is directed to co-injection of air and liquid fuel (typically gasoline) into a direct-injection spark ignition engine. By injecting air with the fuel, it is possible to prevent the over-rich regions that would lead to high emissions. The core of the invention seems to be the use of multiple injection events, combined with the air injection, to achieve a desirable fuel-air mixture prior to ignition. The embodiments discussed refer to a spark ignition engine. This patent teaches the trapping of cylinder gases (as opposed to using a compressed air source) for later use in atomizing the fuel.
U.S. Pat. No. 6,427,660 B1 Aug. 6, 2002 to Yang (assigned to Ford Global Technologies) titled “Dual Fuel Compression Ignition Engine” disclosed the use of low-pressure (15-45 bar) natural gas and diesel co-injection, typically injected prior to top-dead center to operate in a stratified, mostly premixed combustion mode. Split injections are possible depending on the load. The injector incorporates a mixing-chamber into which diesel is injected through a first valve and sits in the chamber until the gaseous fuel valve opens and the gaseous fuel atomizes the diesel and the whole mixture is injected into the combustion chamber. The fact that the gaseous fuel is at moderately low pressure precludes the possibility of late-cycle gaseous fuel injection (peak cylinder pressures in some engines can approach 100 bar). High gaseous fuel pressure (>250 bar) can be a critical part of maintaining high-efficiency and low emissions with exhaust gas recirculation (EGR).
U.S. Pat. No. 5,067,467 November 1991 to Hill et al. (originally assigned to the University of British Columbia) titled “Intensifier-Injector for Gaseous Fuel for Positive Displacement Engines” discloses the idea of using natural gas to continuously atomize diesel in a prechamber without control of the relative timing for liquid pilot and gaseous fuels (i.e., there is no means taught for controlling the liquid/gaseous fuel mass ratio and there is no teaching of anything about metering the liquid fuel or anything about injection phasing). The apparatus described uses a poppet valve injector and the method is described as “gas blast” atomization.
U.S. Pat. No. 6,598,584 B2 Jul. 29, 2003 to Beck et al. (Clean Air Partners Inc.) titled “Gas-Fueled, Compression Ignition Engine with Maximized Pilot Ignition Intensity” relates to pilot-ignition of a premixed natural gas/air charge (commonly referred to as fumigation), the basic concept of which is very old—all the major engine companies have tried variations of this sort. The key novelty disclosed in this patent appears to be the concept of injecting the pilot for a period shorter than the ignition delay or the “mixing time”. Presumably this results in more widespread ignition of the premixed charge and lower emissions. The patent describes in detail the importance of a particular injector geometry (interference angles for the needle-seat seal).
U.S. Pat. No. 6,073,862 Jun. 13, 2000 to Touchette et al., (Westport Research) “Gaseous and Liquid Fuel Injector” includes a detailed review of prior art, including the work of Miyake et al. 1987, who describe a single injector with two concentric needles injecting pilot and high-pressure gaseous fuel through separate holes.
U.S. Pat. No. 4,414,229 Nov. 22, 1983 to Wood (assigned to Southwest Research) “Fuel Injection System for Diesel Engines” describes a dual-fuel injector for liquid fuels. As in the other co-injectors reviewed here, the diesel fuel (pilot) is introduced into a chamber in the injector prior to lifting the needle with the pressure of the second fuel. The concept of injecting the pilot first is discussed with respect to efficient ignition. This invention cannot work for a main injection of gaseous fuel because the needle is actuated by an increase in pressure of the alternative fuel. Fuel injectors cannot be actuated rapidly enough by changes in gaseous fuel pressure because gaseous fuel is so compressible. Also, it appears that the intention is to create a “charge” of diesel fuel (DF) below the alternative fuel (AF) which is all injected essentially sequentially (DF first) when the needle is lifted. There seems to be no way of limiting the DF/AF mass ratio during the early part of the injection.
U.S. Pat. No. 4,742,801 May 10, 1988, to Kelgard “Dual Fuel Mobil Engine System” discloses a system for burning gaseous fuels or liquefied petroleum gas (e.g. propane, LPG) in a diesel engine with a pilot diesel engine using separate injectors for the diesel and gaseous fuel.
U.S. Pat. No. 6,484,699 to Paul et al. teaches a “universal fuel injector” for automatically switching from injecting a combination of two fuels or one fuel when the second fuel is not available. For example, if the second fuel is a gaseous fuel, liquid fuel is introduced through one connection and gaseous fuel is introduced through a different connector. While the '699 patent discloses a liquid fuel distributor, it does not teach anything about metering the liquid fuel or anything about injection phasing.
US 2006/0086825 Application to Date et al. filed 24 Oct. 2005 discloses a fuel injector that co-injects gaseous and liquid fuels. The liquid fuel assists with combustion and lubricates the needle at sliding interfaces and where the needle tip impacts against the seat. The application provides no guidance on how to achieve desirable (or even operable) mass ratios of liquid fuel to gaseous fuel during injections.